The present invention relates to a restraint assembly for controlling movement of a first member relative to a second member. More particularly, a restraint assembly is disclosed that restrains angular movement of the second member relative to the first member with respect to a common axis, but is also compliant in other directions.
A number of devices have been disclosed for measuring forces and moments exerted through a rolling tire and wheel assembly. Co-pending application entitled "MULTI-AXIS LOAD CELL" with application Ser. No. 08/892,914, filed on Jul. 15, 1997, which has been assigned to the same assignee as the present application, and which is hereby fully incorporated by reference, discloses one such apparatus. Generally, the apparatus disclosed therein is a load cell having an inner central hub, an outer ring and a plurality of radially oriented tubes that join the central hub to the outer ring. Measurement sensors, such as strain sensors, are mounted to the plurality of tubes to sense strain therein. In a preferred embodiment, the strain sensors measure eight forces on the plurality of tubes. The eight forces are then transformed to provide forces along and moments about axes of an orthogonal coordinate system. The load cell is particularly well suited for measuring the force and moment components exerted through a rolling tire and wheel assembly. The load cell replaces a portion of the wheel disc, wherein the outer ring is fastened to the rim and the central hub is coupled to a spindle. Power is supplied to and output signals are obtained from the plurality of sensors by a controller through a slip ring assembly. An encoder is coupled to the load cell and provides an angular input signal to the controller indicative of the angular position of the load cell as it rotates. Using the angular input signal, the controller can calculate force and moment components with respect to a static orthogonal coordinate system, for example, a vertical force applied to the wheel assembly even though the load cell is rotating.
In order to properly calculate force and moment components with respect to the static coordinate system, such as the vertical force described above, it is necessary that the input signal from the encoder to the controller be accurate. In other words, any angular displacement of the encoder relative to the wheel rotation would lead to errors in at least some of the calculated force and moment components. Thus, there is a need to hold the encoder fixed with respect to angular displacement. However, there is also a need to allow some movement of the encoder, for example, as the wheel assembly moves up and down or experiences cornering loads.